How do I connect a SLR (Single-Lens Reflex) camera to my telescope?

To connect an SLR camera to your telescope, you’ll need two accessories: a camera T-ring and a T-adapter. T-ring is also known as T2 mount, and T-adapter is sometimes known as T-mount. This system is a worldwide standard 42mm thread to connect cameras to other devices.

A T-adapter attaches to the scope and a T-ring attaches to your SLR camera. A T-adapter with a 1.25” eyepiece barrel is very versatile and slips into the eyepiece drawtube of most telescopes. Other types of T-adapters with threads are specific to certain types of scopes. (Specialized accessories like a radial guider or tele-extender have T-threads that take T-rings, so they act like specialized T-adapters). For example, a T-adapter has been purposely designed to connect various SLR cameras to the Nipon 25-125x92 spotting scope.

The threads on the T-adapter fits into all T-rings. Since each brand of camera has its own specific thread size or bayonet type, you need the proper T-ring. Thus Canon has its T-rings (two of them); Nikon has its own T-rings; Minolta has their own specific rings, and so on. Some T-rings are available here for most popular brands, such as Sony, Olympus 4/3, Olympus Micro 4/3, Pentax K, in addition to those mentioned earlier.

To attach SLR cameras to your telescope, first, remove the visual accessories you are using – eyepiece, diagonal, visual back. Then either screw on or insert the correct T-adapter for your scope and the type of photography you want to do.

For example, to use the T-adapter with the 1.25” barrel, remove your SLR's lens and attach the T-ring to your camera, then the T-ring to the T-adapter and slide the 1.25” barrel into your eyepiece holder. Add a shutter release and the camera is now ready for prime-focus photography. Your telescope acts as a platform and can be used to provide tracking if the scope has been polar aligned. Tracking may not be needed for very short exposures of the sun, moon and planets.

Important Note: For some Newtonian telescope models, the focal plane of the telescope may not be far enough from the tube to allow you to focus with the T-adapter/camera setup you are using. Try using a T-adapter with a built-in Barlow lens (with the lens at the forward end), such as this Nikon SLR adapter, to extend the focal plane to reach your camera’s imaging plane. Another way that will achieve infinity focus with almost any Newtonian or other telescope is eyepiece projection directly into your camera with a large 32mm, 40mm, or 10-30mm zoom eyepiece. Some eyepieces have even got T-threads under the rubber eyecup, so simply thread it into your camera T-ring and then attach to your camera and put the assembly into your scope’s eyepiece drawtube.

More information can be found from this link: Digiscoping

How much magnification can I use, and how much is too much?

Telescope magnification is actually a relationship between two independent optical systems – the telescope itself and the eyepiece you are using. To determine power, divide the focal length of the telescope (in mm) by the focal length of the eyepiece (in mm). By exchanging an eyepiece of one focal length for another, you can increase or decrease the power of the telescope. For example, a 25 mm eyepiece used on a 1250 mm focal-length telescope would yield a power of 50x (1250/25 = 50) and a 10 mm eyepiece used on the same instrument would yield a power of 125x (1250/10 = 125). Since eyepieces are interchangeable, a telescope can be used at a variety of powers.

There are practical limits of magnification for telescopes. These are determined by the laws of optics and the nature of the human eye. As a rule of thumb, the maximum usable power is equal to 50-60 times the aperture of the telescope (in inches) under ideal conditions. Powers higher than this usually shows a dim, lower contrast image. For example, the maximum power on a 127 mm telescope (5” aperture) is in the range 250x - 300x. As power increases, the sharpness and detail seen will be diminished. The higher powers are mainly used for lunar, planetary, and binary star observations.

Most of your observations will be done with lower powers (6 to 25 times the aperture of the telescope in inches). With these powers, the images will be much brighter and crisper, providing more enjoyment and satisfaction with the wider fields of view.

A good way to increase magnification is to use a Barlow lens. A Barlow lens rated at 2x can be used with your existing eyepiece and it will double the magnification of any existing eyepiece.

How do I use eyepieces with my telescope?

Your eyepieces are the first accessories you should have and use with your telescope. Since they are interchangeable, a telescope can be used at a variety of powers.

Look through the eyepiece by placing your eye just behind it to take advantage of its eye relief, the spacing between the lens and your eye. This should be at least 15 mm for the best comfort, maybe more if you wear eyeglasses. You’ll lose field of view if you place your eye farther away and may even move your eye out of the beam of light from the eyepiece. Viewing too close to the eyepiece will prevent you from blinking and may also cause a black ring to appear around the field of view.

Now turn the focus knob of the telescope, first one way then the other until the object is in focus.

Always start with the lowest power eyepiece (i.e., the one with the highest number in millimeters printed on it). It is much easier to focus and has a wider field of view, making it easier to aim the telescope at a distant target.

As power increases, the sharpness and detail seen will be diminished. The higher powers are mainly used for lunar, planetary, and binary star observations.

Most of your observations will be done with lower powers. With these lower powers, the images will be much brighter and crisper, providing more enjoyment and satisfaction with the wider fields of view.

A good way to increase magnification is to use a Barlow lens. A Barlow lens rated at 2x can be used with your existing eyepiece and it will double the magnification of any existing eyepiece. Since longer-focal-length eyepieces generally have longer eye relief, using a Barlow to increase magnification will allow more comfortable high-power viewing.

A basic set of eyepieces would be 32 mm, 20mm (or 26mm), and 10mm (or 16mm), plus a Barlow (2x or 3x power).

How to determine a telescope's magnification?

The magnification of a telescope changes as the eyepiece is changed. Magnification can be calculated by dividing the focal length of your telescope by the focal length of the eyepiece.

Calculating magnification = Telescope's focal length / Eyepiece focal length

Always start with your lowest magnification eyepiece (longest focal length) and work upwards from there.

A 2x Barlow lens will double the magnification of whatever eyepiece you use with it while preserving its eye relief. For example: using a telescope with a 800 mm focal length with a 16 mm eyepiece will give you 50x magnification. Using the same telescope and eyepiece with a 2x Barlow lens will give 100x magnification. This would be the same magnification as a 800 mm telescope with a 8 mm eyepiece.